This invention relates to liquid toners for use in a combination of electrostatic copier and lithographic printer generally known as a copier duplicator, and more particularly to compositions of toners wherein finely divided pigment, dye, polymer and a hydrophobic agent are suspended in a volatile hydrocarbon liquid having a high electrical resistance.
In electrostatic printers, a sheet having a photoconductive layer is given a electrostatic positive or negative charge in the dark, such as by means of a corona-charging device. The charge layer is then exposed to a light image of an original document to cause the charge on the layer to leak off in non-image areas and selectively leave a latent electrostatic charge image. This latent image is then developed by applying to the photoconductive layer a toner containing particles which have a charge opposite to the residual electrostatic charge image so that the toner particles adhere to the charged areas and form an image. In order to function properly for this purpose, the toner must be capable of producing a colored layer of suitable density on the charged areas without unduly coloring the background areas. Although there are many liquid toners which serve satisfactorily in the electrophotographic production of a single copy, where multiple copies are to be made, as in a copier duplicator, for various reasons prior toners have proven deficient.
In a copier duplicator the sheet having the image serves as a master in a combination electrophotographic and lithographic operation where many copies are to be produced. This includes the operation where the master may be part of an offset printer. In such an operation, a sheet having a photoconductor coating is given a charge as by a corona flash. The charged surface is then exposed to an original to be reproduced and an image is formed on the photoconductor surface. The sheet is then passed through a liquid toner whereby hydrophobic, oleophilic particles are electrostatically attached to the latent image. The master is then dried to set the toner, etched to render the background hydrophilic, dampened with water and then dampened with an oil based ink. In an offset operation the image is then transferred to a blanket from which it is subsequently transferred to the copy paper.
In a copier duplicator, the toner must not only obtain true reproduction over the image area, otherwise known as "fill-in", but it should also be highly hydrophobic and oleophilic as well as be impervious and resistant to etching chemicals.